1. Field of the Invention
The present invention relates to a method for resolving an issue regarding channel access due to an introduction of a directional antenna for handling a path loss, and maximizing a spatial reuse gain in a wireless communication system in which data may be transmitted at a relatively high speed through use of an ultra-wideband frequency band.
2. Description of the Related Art
A Carrier Sense Multiple Access with Contention Avoidance (CSMA/CA) scheme for a wireless local area network (LAN) system using a frequency band of 2.4 GHz or 5 GHz has been developed on the assumption of using an omnidirectional antenna and thus, may involve several issues when a directional antenna is used. A transmission through the directional antenna may concentrate a signal in a predetermined direction, thereby extending a signal reach distance in comparison with the omnidirectional antenna, and may enable concurrent communication in different directions using a spatial reuse gain. However, a system performance may deteriorate due to increases in a deafness issue and a hidden node issue. Even though the hidden node issue may occur when the omnidirectional antenna is used, the hidden node issue may be effectively resolved by transmitting a ready to send (RTS) control frame and a clear to send (CTS) control frame before exchanging a DATA/acknowledgement (ACK) packet.
Here, a deafness issue may refer to a state in which a reception node fails to receive an RTS control frame of a transmission node. When a reception node fails to receive an RTS control frame of a transmission node, the node transmitting the RTS control frame may attempt retransmission of the RTS control frame. In this instance, the transmission node may double a contention window of the transmission node according to a CSMA/CA protocol, thereby delaying a channel access time. Due to a continuous deafness, data packets to be transmitted may be deleted in a repeated manner.
The hidden node issue may refer to an issue of degrading a system performance due to packets including an RTS control frame that create errors in communication occurring around the corresponding node. Here, the packets may be transmitted by the corresponding node not recognizing communication occurring around the corresponding node.
Nowadays, a millimeter wave communication system based on a 60 GHz frequency band is being developed on the assumption of using a directional antenna due to a millimeter wave propagation characteristic. The millimeter wave communication system may perform a beamforming process to set a link to a destination device when the directional antenna is used. The beamforming process may correspond to a process of generating a plurality of beams being used in a predetermined area, identifying a predetermined destination device by transmitting signals in all directions, successively using beams, and then forming a link for a data transmission by forming relatively delicate beams. The millimeter wave communication system recognizing a CSMA/CA issue occurring when a directional antenna is used may schedule a time division multiple access (TDMA) resource allocation using a central control unit such as an access point (AP), and may enable device pairs predetermined in a scheduled TDMA resource to communicate, thereby resolving the CSMA/CA issue. However, when traffic is generated intermittently, a TDMA scheme may not use resources effectively and thus, the TDMA scheme may be used in combination with a CSMA/CA scheme. To effectively apply the CSMA/CA scheme to the millimeter wave communication system, a spatial reuse gain may be maximized while resolving issues described in the foregoing.